Re: [PATCH] drm/i915: cache hw power well enabled state

[Imre Deak <imre.deak@intel.com>]

On Fri, 2014-06-06 at 19:19 +0200, Daniel Vetter wrote:
> On Thu, Jun 05, 2014 at 08:31:47PM +0300, Imre Deak wrote:
> > Jesse noticed that the punit communication needed to query the VLV power
> > well status can cause substantial delays. Since we can query the state
> > frequently, for example during I2C transfers, maintain a cached version
> > of the HW state to get rid of this delay.
> > 
> > This fixes at least one reported regression where boot time increased by
> > ~4 seconds due to frequent power well state queries on VLV during eDP
> > EDID read.
> > 
> > Reported-by: Jesse Barnes <jesse.barnes@intel.com>
> > Signed-off-by: Imre Deak <imre.deak@intel.com>
> 
> A citation for the regressing commit here (i.e. the one that enabled vlv
> runtime pm) would be good so that Jani can pick it up.

I'm not aware of any other case where we had a significant overhead, so
for the above particular issue I'd say

this was introduced by

commit bb4932c4f17b68f34645ffbcf845e4c29d17290b
Author: Imre Deak <imre.deak@intel.com>
Date:   Mon Apr 14 20:24:33 2014 +0300

    drm/i915: vlv: check port power domain instead of only D0 for eDP
VDD on

> Aside: intel_rpm.c with the runtime pm infrastructure + some overview
> kerneldoc would be really, really nice.

You mean to move out the power well and rpm stuff to this new file?
Agreed, intel_pm.c is rather big already.

--Imre